定從要學好，刪繁就簡系首要，明確先行詞，然后定關系詞調；
指人主格用who，賓格whom好，事物用which，主/賓都可靠；
用that引定從，人/物均需要，非限制性定從句，切勿用that導；
關系詞作賓語，常將其省略掉，若介詞+關系詞，關系詞切勿拋，無論人/事物，who/that均不導，指人必whom，事物which邀；
as引定從，（部分）主句內容包，常含“正如”意，位置任意挑；
which如此用，用時思量好，有時含“消極”味，主句之后到；
such/ the same + as，固定搭配好，特殊用法務牢記，勿用亂了套；
whose作定語，人/物它全包，n. + of + whom/which，可與其對調。
二、只用that作關系代詞的幾種情況
先行（詞）本身系數詞，不定代詞指事物，
人與事物共先行，There be中指物詞作主語，
關系詞定從中作表語，問句避免疑問詞重復，
另有序數詞/最高級，every/ the very/ the only，
以及不定代詞若干個，名詞前把事物來修飾，
以上情況請記清，只能使用that引導定從句。
[鞏固練習]
請在橫線上添上恰當的關系詞。
1. We need comrades _____________ can help us.
2. The man _____________ you saw yesterday was a doctor from Beijing.
3. This is a story about a communist fighter _____________ name或the name of _____________ is Liu Hu-lan.
4. This is our classroom， _____________ windows或the windows of _____________ face the south.
5. Here is a book _____________ will give a lot of useful knowledge.
6. This is the song _____________ we like best.
7. I will never forget the day， on _____________ I first saw him.
8. This is the room _____________ Lao Liu once lived in.
9. Do you still remember the day on _____________ he joined the army？
10. The earth， _____________ we all know， moves around the sun.
11. _____________ is known to all， the earth is round.
12. The sun is bigger than the earth， _____________ is known to us all.
13. He did not study hard， _____________ led to his failure.
14. We used the same type of machine _____________ they did.
15. We have found such materials _____________ are used in their factory.
16. Here are five fish. The two _____________were caught yesterday are gold fish.
17. Everything _____________ I told you just now is true.
18. They talked of the things and persons _____________ they remembered in the school.
19. There are stars _____________ we still don‘t know in space.
20. Li Ying is not the girl _____________ she used to be ten years ago.
[試題答案]
1. who/that 2. who/whom/that/×
3. whose； whom 4. whose； which
5. which/ that 6. which/ ×
7. which 8. that/which/ ×
9. which 10. as
11. As 12. as/ which
13. which 14. as
15. as 16. that
17. that/ × 18. that/×
19. that/× 20. that
